1. Field of the Invention
The present invention relates to a resin composition for forming an optical waveguide to be used as a material for forming, for example, a clad layer constituting an optical waveguide in an optical waveguide apparatus to be widely used in optical communication, optical information processing, or any other general optics such as an opto-electric hybrid board, and to an optical waveguide using the composition.
2. Description of the Related Art
A material for forming an optical waveguide for an opto-electric hybrid board is required to have characteristics such as high flexibility and a low refractive index in accordance with its use applications. Further, low tackiness has become an essential characteristic in order that the material may be adapted to a roll-to-roll (R-to-R) process with an eye toward mass production.
In general, a reduction in elastic modulus of a material for forming a clad layer of an optical waveguide has been conventionally performed for imparting high flexibility. In addition, for the reduction in elastic modulus, a material obtained as described below is used as the material for forming the clad layer. A phenoxy resin as an aromatic, long-chain, bifunctional epoxy resin having tough characteristics is used as a binder resin and the binder resin is blended with a long-chain, bifunctional resin having a main skeleton (such as an aliphatic skeleton) that imparts flexibility. Thus, the reduction in elastic modulus is achieved.
However, such blending design as described above is liable to show the following tendency. The refractive index of the clad layer increases owing to the use of the aromatic binder resin, with the result that an optical loss at the time of bending needed for a material for forming an optical waveguide for an opto-electric hybrid board deteriorates. In addition, when an aliphatic, bifunctional resin capable of imparting a low refractive index is added to compensate for the increase in refractive index, the following problem of a trade-off arises. The addition sacrifices bending property and tackiness (see, for example, JP-A-2010-243920 and JP-A-2010-164770).
Against such technological background, a forming material that brings together high flexibility (bending resistance), a low refractive index, and low tackiness at the time when the material is uncured has been strongly desired as a material for forming a clad layer.